This invention relates to an improvement in an inertia supercharger for use in multi-cylinder internal combustion engines.
In the multi-cylinder internal combustion engines such as diesel engines, there has heretofore been employed an inertia supercharger wherein the air intake ports of the engine are fitted with an air intake manifold and the dynamic effect or inertia of the air supplied through the air intake manifold is utilized to increase the amount of the air supplied into the cylinders thereof.
The length of the above-mentioned air intake manifold may depend on such factors as the cylinders volume, the timing of actuation of air intake and exhaust valves, the sectional area of the air intake manifold and the number of revolutions of the engine to be tuned with the operation of the supercharger and may be approximately obtained by the following formula: ##EQU1##
where .gamma. is the frequency of the air supplied into the intake manifold; a is the velocity of the sound in the supplying air; F.sub.pip is the inner sectional area of the air intake manifold; V.sub.h is the effective volume of the cylinder; and l is the length of the air intake manifold including the air intake ports.
In order to obtain a significant inertia effects, it is required to satisfy the following formula: ##EQU2## where N.sub.e is the rotational speed of the engine and .theta..sub.s is the effective opening angle of the air intake valve.
Regarding the inner sectional area of the air intake manifold F.sub.pip, its proper range of values can be obtained by optimizing the mean velocity of the air supplied through the intake manifold at or around the tuned engine speed. The mean velocity of the air drawn through the intake manifold can be obtained by the following formula: ##EQU3## where V.sub.a is the mean velocity of the air flow through the intake manifold; S is the stroke of the piston; and F.sub.pis is the sectional area of the piston. In the vicinity of the number of revolutions of the engine to be tuned with the operation of the supercharger, the value of V.sub.a should preferably be 50 to 60 meters per second and the inner sectional area of the air intake manifold F.sub.pip is determined so that V.sub.a may be kept within such a range. Further, in order to prevent a decrease in the dynamic effect of the supplied air due to the resistance of air cleaner etc., it is necessary to provide a surge tank between each air intake manifold and the air cleaner. An experimental result that the minimum required volume of the surge tank may correspond to the total exhaust volume of the engine was obtained.
If and when the inertia supercharger with the air intake manifold, the length of which is determined by the above-mentioned formula, is fitted to the air intake ports of the engine, its volumetric efficiency can be remarkably improved near the number of revolutions of the engine tuned with the supercharger as compared with those of air intake manifolds normally used thereby enabling a substantially improved supercharging efficiency to be obtained. Conventional inertia superchargers have been disadvantageous in that because air intake manifolds used therein are in the form of straight pipes and surge tanks are connected to the leading ends of the manifolds and hence the assemblies project considerably to the side of the engine thereby interfering sometimes with the installation of other machines and equipments and spaces for installing the inertia superchargers must be secured in advance.
In order to eliminate such disadvantages, a counter-measure was taken as a trial by using bent pipes as the air intake manifold. However, in the case of construction vehicles each having a comparatively low speed engine mounted thereon which requires an intake manifold longer than those of high speed engines, a difficulty has been encountered that even if the air intake manifold in the form of bent pipes are employed it contacts with the bonnet in some cases.